Carol II (15 October 1893 – 4 April 1953) reigned as King of the Romanians from the abdication of his father on 1 December 1918 until his death on 4 April 1953. He was the first member of the Romanian royal family to be raised in the Orthodox faith.

Carol was born in Peleș Castle. In November 1914, Carol joined the Romanian Senate, as the 1866 Constitution guaranteed him a seat there upon reaching maturity. Known more for his romantic misadventures than for any leadership skills, Carol (Romanian for "Charles") was first married in the Cathedral Church of Odessa, Ukraine, 31 August 1918, to Joanna Marie Valentina Lambrino (1898–1953), known as "Zizi", the daughter of a Romanian general. The marriage was annulled on 29 March 1919 by the Ilfov Suburban Court. Carol and Zizi continued to live together after the annulment. Their only child, Mircea Gregor Carol Lambrino, was born 8 January 1920.

When Romania concluded peace with the Central Powers in May 1918 his father King Ferdinand refused to sign it. This created a crisis in Romania as the Central Powers did not consider the war ended until the king signed it. Carol, unaware of the full text of the treaty, was in favour of it as it united Bessarabia with Romania. The government of Alexandru Marghiloman pressured King Ferdinand to abdicate on 1 December 1918. Carol was proclaimed King the same day.

Carol next married, in Athens, Greece, on 10 March 1921, Princess Helen of Greece and Denmark. They were second cousins as both were great-grandchildren of Queen Victoria. The marriage soon collapsed in the wake of Carol's affair with Elena "Magda" Lupescu (1895?–1977), the Roman Catholic daughter of a Jewish pharmacist and his Roman Catholic wife. Magda Lupescu had formerly been the wife of Army officer Ion Tâmpeanu. Helen wanted to divorce Carol but was persuaded against it for the sake of unity in the monarchy when the country was fragile.

For the next two decades, to compensate for his rather negative and well-deserved "playboy king" image, Carol created a lavish personality cult around himself that grew more extreme as his reign went on, which portrayed the king as a Christ-like being "chosen" by God to create a "new Romania". In the 1934 book The Three Kings by Cezar Petrescu, which was intended for a less educated audience, Carol was constantly described as being almost god-like, the "father of the villagers and workers of the land" and the "king of culture" who was the greatest of all the Hohenzollern kings.

After the Great Depression hit Romania, he sought to influence the course of Romanian political life, first through manipulation of the Liberal party and anti-Semitic factions, and subsequently by choosing a ministry of his own in January 1938.